Used a .223 for a couple mulies. Penetration was a LOT more than most seem to believe it would be. No sign of the 'explodes just under the skin' stuff that folks keep repeating.
Least powerful? Likely the .45 cal round ball muzzle loader I took a WT doe with. ~40 grains of Pyrodex, by memory, still got a pass through the doe, diagonally. In behind the ribs on one side, out through the front shoulder on the other. No real damage besides the hole. No meat loss!
Cheers
Trev